Method and system for compensating for phase variations caused by transmitter activation

ABSTRACT

A method and apparatus that reduces the amount of constellation rotation due to power amplifier (PA) insertion phase variation during activation (i.e., turn on) of a transmitter. This is accomplished by applying an instantaneous phase rotation during the transmitter turn on at digital baseband to counteract and minimize unwanted phase variations.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. provisional application No.60/562,664, filed Apr. 15, 2004, which is incorporated by reference asif fully set forth.

FIELD OF THE INVENTION

The present invention generally relates to wireless communicationsystems. More particularly, the present invention relates to digitalsignal processing (DSP) techniques used to compensate for phasevariations due to activating a transmitter.

BACKGROUND

In a conventional time division duplex (TDD) system, a transmitterwithin the system is temporarily deactivated during receive time slotsin order to reduce power consumption. However, once a turn on command isinitiated, the bias current of a power amplifier (PA) in the transmitterrequires a significant amount of time to move from its shut down valueto its desired quiescent value. This type of time varying bias resultsin a proportional change in the PA insertion phase, which in turn willresult in a rotation of the signal constellation.

An insertion phase variation will occur even if the input power of thetransmitter is held constant. As a result, performance degradation ofphase sensitive receiver algorithms at the beginning of time slots willoccur unless the insertion phase variation is reduced and kept withinsome acceptable level when the transmitter is activated (i.e., turnedon). A method and system for compensating for phase variations caused byactivating the transmitter is desired.

SUMMARY

The present invention provides a method and a system that reduces theamount of constellation rotation due to insertion phase variation.

The insertion phase variation is adjusted when a transmitter or a poweramplifier therein is turned on (i.e., activated). This is accomplishedby incrementally applying an instantaneous phase rotation duringtransmitter turn on at digital baseband to counteract and minimizeunwanted phase variations. The present invention is applicable to TDD,frequency division duplex (FDD), orthogonal frequency divisionmultiplexing (OFDM), code division multiple access (CDMA) and timedivision synchronous CDMA (TDSCDMA) systems.

The transmitter includes at least one amplifier which causes theinsertion phase deviation when transitioning from a deactivated state toan activated state, and means for establishing a period for thetransmitter to transition to a quiescent state value associated with theactivated state. The transmitter further includes a means for setting atarget insertion phase that corresponds to the quiescent state value,and means for incrementally adjusting the insertion phase of thetransmitter until the quiescent state value is equal to the targetinsertion phase when the amplifier is activated.

The means for incrementally adjusting the insertion phase of thetransmitter includes an accumulator and a function unit (e.g., a look uptable (LUT)) in communication with the accumulator. The function unitoutputs at least one insertion phase rotation control function inresponse to power gain command values accumulated by the accumulator.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred example, given by way of exampleand to be understood in conjunction with the accompanying drawingwherein:

FIG. 1 is a block diagram of a radio transmitter operating in accordancewith the present invention;

FIG. 2 is a timing diagram showing time slots separated by a guardperiod during which the transmitter of FIG. 4 may be activated; and

FIG. 3 is a flow chart of a process including steps implemented tocontinuously counteract the effects of phase offsets introduced into thetransmitter of FIG. 1 due to the powering up of an amplifier therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a method and system that performs phaseinsertion adjustments in a transmitter when it transitions from adeactivated state to an activated state.

Preferably, the method and system disclosed herein is incorporated intoa wireless transmit/receive unit (WTRU). Hereafter, a WTRU includes butis not limited to a user equipment, mobile station, fixed or mobilesubscriber unit, pager, or any other type of device capable of operatingin a wireless environment. The features of the present invention may beincorporated into an integrated circuit (IC) or be configured in acircuit comprising a multitude of interconnecting components.

The present invention is applicable to communication systems using timedivision duplex (TDD), frequency division duplex (FDD), code divisionmultiple access (CDMA), CDMA 2000, time division synchronous CDMA(TDSCDMA), orthogonal frequency division multiplexing (OFDM) or thelike.

FIG. 1 is a block diagram of a transmitter 100 operating in accordancewith the present invention. The transmitter includes a pair of digitalto analog converters (DACs) 105, 110, a modulator 115, a radio frequency(RF) variable gain amplifier (VGA) 120 and a PA (power amplifier) 125.The RF VGA 120 and PA 125 are selectively enabled and disabled bycontrol line 130. Furthermore, the transmitter 100 includes multipliers135, 140, 145, 150 and adders 155 and 160. The transmitter 100 generatessignals based on a real (Re) I signal component 165 and an imaginary(jIm) Q signal component 170. The phase of the signal components Re andjIm by x degrees (e^(jx)) are rotated as described by Equation 1 below:(Re+jIm)×e ^(jx)=(Re+jIm)×(Cos (x)+j Sin (x))  Equation 1

The transmitter 100 deactivates the RF VGA 120, the PA 125 and otherpower consuming components of the transmitter 100 during the occurrenceof receive time slots in a TDD type system, thus essentiallydeactivating the transmitter 100. Based on the condition of control line130, and the output 174 of an accumulator 173, a function unit (e.g., anLUT) 175 is used to provide a phase offset (x) to compensate for phasevariations caused by deactivating or activating the transmitter 100.Alternatively, other devices and/or techniques may be used in lieu ofthe accumulator 173.

FIG. 2 is a timing diagram 200 showing a receive time slot 205 and atransmit time slot 210 separated by a guard period 215 during whichtransmitter (i.e., amplifier) switching 220 occurs.

FIG. 3 is a flow chart of a process 300 including steps implemented tocontinuously counteract the effects of phase offsets introduced into thetransmitter 100 due to the powering up of at least one amplifiertherein. In step 305, a period is established for adjusting the outputpower level of the transmitter 100, and at least one power amplifiertherein, for the transmitter 100 to transition from a deactivated state(“OFF”) value to a desired quiescent (“ON”) state value when thetransmitter 100 is activated. The insertion phase of the transmitter 100will overshoot the “ON” value and eventually settle. In step 310, areference target insertion phase is set that corresponds to thequiescent state value of the transmitter 100. The function unit 175detects a change on the control line 130 and instantaneously adjusts theinsertion phase of the transmitter 100 by inputting incremented and/ordecremented power gain control values into the accumulator 173 via anaccumulator input 176. The same power gain control values are providedto the RF VGA 120. The transmitter 100, and thus the amplifiers 120,125, therein, are activated (i.e., turned on) during the guard period215. Because it takes a substantial amount of time for an applied AGCincremented value to settle in the transmit chain, the transmitter 100is required to provide sufficient time periods for implementing ramp upand ramp down of the transmitter 100.

In step 315, an incremented power gain command value provided on input176 is input into accumulator 173. In step 320, the accumulator 173outputs an accumulated value 174 to the function unit 175. In step 325,the function unit 175 outputs one or more rotation functions of “x”,(e.g., sin (x), cos (x)), to instantaneously adjust the phase of thetransmitter 100. In step 330, a determination is made as to whether theaccumulated value output 174 is equal to the target insertion phase. If,in step 330, the accumulated value output 174 is determined not to beequal to the target insertion phase, the process 300 repeats steps 315,320, 325 and 330 until the accumulated value 174 is determined to beequal to the target insertion phase.

In a preferred embodiment of the present invention, the function unit175 at digital baseband instantaneously adjusts the insertion phase ofthe transmitter 100 by providing a value of “x” such that it issufficiently close to the desired quiescent value at the time oftransmitter switching. The value of “x” is then gradually reduced tozero such that the overall insertion phase deviation is maintained fromthe quiescent value to within some acceptable amount. In order toprovide both continuous and discrete phase adjustments, the accumulator173 may be used to indicate to the function unit 175 what the currentpower is by summing up several incremented and/or decremented power gaincontrol values 176.

While this invention has been particularly shown and described withreference to preferred embodiments, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the scope of the invention describedhereinabove.

1. In a transmitter including at least one amplifier, a method ofcontrolling insertion phase deviation of the transmitter caused by theamplifier transitioning from a deactivated state to an activated state,the method comprising: (a) establishing a period for the transmitter totransition to a quiescent state value associated with the activatedstate; (b) setting a target insertion phase that corresponds to thequiescent state value; and (c) incrementally adjusting the insertionphase of the transmitter until the quiescent state value is equal to thetarget insertion phase when the amplifier is activated.
 2. The method ofclaim 1 wherein the transmitter is comprised by a time slot-basedcommunication system, and the established period is a guard period thatoccurs between a receive time slot and a transmit time slot.
 3. Atransmitter for controlling insertion phase deviation, the transmittercomprising: (a) at least one amplifier which causes the insertion phasedeviation when transitioning from a deactivated state to an activatedstate; (b) means for establishing a period for the transmitter totransition to a quiescent state value associated with the activatedstate; (c) means for setting a target insertion phase that correspondsto the quiescent state value; and (d) means for incrementally adjustingthe insertion phase of the transmitter until the quiescent state valueis equal to the target insertion phase when the amplifier is activated.4. The transmitter of claim 3 wherein the transmitter is comprised by atime slot-based communication system, and the established period is aguard period that occurs between a receive time slot and a transmit timeslot.
 5. The transmitter of claim 3 wherein the means for incrementallyadjusting the insertion phase of the transmitter comprises: (i) anaccumulator; and (ii) a look up table (LUT) in communication with theaccumulator, wherein the LUT outputs at least one insertion phaserotation control function in response to power gain command valuesaccumulated by the accumulator.
 6. A wireless transmit/receive unit(WTRU) for controlling insertion phase deviation, the WTRU comprising:(a) at least one amplifier which causes the insertion phase deviationwhen transitioning from a deactivated state to an activated state; (b)means for establishing a period for the amplifier to transition to aquiescent state value associated with the activated state; (c) means forsetting a target insertion phase that corresponds to the quiescent statevalue; and (d) means for incrementally adjusting the insertion phase ofthe WTRU until the quiescent state value is equal to the targetinsertion phase when the amplifier is activated.
 7. The WTRU of claim 6wherein the WTRU operates in conjunction with a time slot-basedcommunication system, and the established period is a guard period thatoccurs between a receive time slot and a transmit time slot.
 8. The WTRUof claim 6 wherein the means for incrementally adjusting the insertionphase of the WTRU comprises: (i) an accumulator; and (ii) a look uptable (LUT) in communication with the accumulator, wherein the LUToutputs at least one insertion phase rotation control function inresponse to power gain command values accumulated by the accumulator. 9.An integrated circuit (IC) for controlling insertion phase deviationtherein, the IC comprising: (a) at least one amplifier which causes theinsertion phase deviation when transitioning from a deactivated state toan activated state; (b) means for establishing a period for theamplifier to transition to a quiescent state value associated with theactivated state; (c) means for setting a target insertion phase thatcorresponds to the quiescent state value; and (d) means forincrementally adjusting the insertion phase until the quiescent statevalue is equal to the target insertion phase when the amplifier isactivated.
 10. The IC of claim 9 wherein the IC operates in conjunctionwith a time slot-based communication system, and the established periodis a guard period that occurs between a receive time slot and a transmittime slot.
 11. The IC of claim 9 wherein the means for incrementallyadjusting the insertion phase of the IC comprises: (i) an accumulator;and (ii) a look up table (LUT) in communication with the accumulator,wherein the LUT outputs at least one insertion phase rotation controlfunction in response to power gain command values accumulated by theaccumulator.